46 



HYDRATES IN AQUEOUS SOLUTION. 



POTASSIUM FERRICYANIDE. 



The freezing-point lowerings were small, and therefore the 'salt showed no 

 hydration. 



DISSOCIATION OF POTASSIUM FERRI CYANIDE. 



Light could be thrown on the icay in which potassium ferricyanide disso- 

 ciated, by comparing the conductivity of this salt with that of potassium 

 ferrocyanide at the same dilutions. The differences were just about what 

 would be expected, as will be seen below, if the solutions of the ferrocya- 

 nide contained one more molecule of potassium cyanide than those of the 

 ferricyanide. From this and the result obtained with the ferrocyanide, we 

 conclude that potassium ferricyanide dissociates thus: 



K 3 Fe(CN) 6 = K,CN,K,CN,K,Fe(CN) 4 . 



This is also in accord with the value found for //.GO for this substance. 

 TABLE 25. POTASSIUM FERRICYANIDE. 



POTASSIUM FERROCYANIDE. 



This salt was chosen on account of the statement in the literature that 



+ + + + EEEEEE 



it dissociates thus, K, K, K, K, Fe(CN) 6 , yielding 5 ions. We shall see 

 that this is probably wrong. The molecular lowerings of the freezing-point 

 that were produced were small; indeed, so small 

 that there was no evidence of any appreciable 

 hydration in the solutions. We then took up the 

 problem as to whether there is any appreciable, 

 time factor in the conductivity of solutions of potas- 

 sium ferrocyanide. Solutions of the salt were 

 prepared and their conductivities determined at 

 25, as is shown in the accompanying table. After 



making these measurements the solutions were allowed to remain in the 

 thermostat-bath for thirty minutes, and their conductivities redetermined. 



